This article examines Machiavelli’s writings on fortresses as a new starting point for a genealogy of urban fortification. In contrast to theorists of Machiavelli who approach fortresses as defensive structures that preserve the present political order, this article considers fortresses as weapons to privatize civic life. It explores the significance of fortresses for democratic readings of Machiavelli, suggesting that Machiavelli offers a careful analysis of the spatial organization of power and its implications for popular self-government. This reconsideration of fortresses in Machiavelli brings his political thought into conversation with contemporary urban theorists critical of the enclosure of public space. The article argues that Machiavelli seeks to resignify notions of fortification and replace the construction of fortresses with practices of fortifying publics. Such practices find ways to strengthen public spaces and envision durable democracy.